Strain-induced microstructure development due to a wetting phenomenon in the Co–Pt system Original Research Article

In the Co–Pt system, a cooling experiment can drive a sample ordered in the cubic L12 structure inside the two-phase region involving L12 and the tetragonal L10 structure. We had shown previously (Phys. Rev. B. 61(5) (2000) 3317) that the first step of the microstructural development is the decoration of the antiphase boundaries (APBʹs) in the L12 structure by a thin L10 layer. Using transmission electron microscopy observations, we present here the later stages of the microstructural evolution, i.e. when the cooling procedure induces a larger amount of L10 structure in the sample. Depending on the aging temperature, the final microstructure consists of large L12 domains separated by either thick platelets of the L10 structure, or by a saw-tooth like morphology. We explain these microstructural developments by a theoretical analysis of the accommodation of the elastic stresses generated by the difference in symmetry and lattice parameters between the L12 and L10 structures.